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Heart Surgery

How the heart works

The heart is a hollow muscular organ about the size of a closed fist. It’s in the centre of your chest, behind the breastbone. Each heartbeat sends blood that’s rich in oxygen and nutrients to all parts of your body.

The heart has 2 sides and 4 chambers — 2 chambers on the right and 2 on the left. The upper chambers are called atria and the lower chambers are called ventricles.


The right atrium receives the blood that has circulated through the body.

How the Heart Works Cred​it: Alberta Health Services

The left atrium receives the blood that has circulated through the lungs.

The atria’s main job is to hold the blood they collect while the ventricles are pumping and the valves between the atria and ventricles are closed.


The right ventricle pumps blood into the lungs to be loaded with oxygen. The left ventricle pumps the blood out to all other organs and the rest of the body.

Because the left ventricle must work harder to create the blood flow at high pressure (the blood pressure) throughout the body, the left ventricle muscles is much thicker and stronger than the right ventricle muscle.

Heart Valves
Cred​it: Alberta Health Services

Heart valves

The 4 chambers of the heart are separated by valves.

The valves open to let blood flow forward through the chambers and close so that the blood can’t flow backwards.

When the ventricles are finished contracting, the valves open, and the blood in the atria flows into the ventricles, helped by the pumping of the atria.

Coronary arteries

The heart needs a constant supply of oxygen to work well. The heart muscle receives its blood, oxygen, and nutrients from the coronary arteries.

Coronary Arteries Cred​it: Alberta Health Services

There are 2 main coronary arteries, the left and the right.

The left main artery divides into 2 main branches:

  • Left anterior descending artery, which brings blood to the front of the heart.
  • Circumflex artery, which wraps around the heart and brings blood to the left side and back of the heart.

The right coronary artery brings blood to the right side and back of the heart.​​​​

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